1. Field of the Invention
The present invention relates to a process and a apparatus for non-agitated flotation of substances with a low degree of hydrophoby and/or low stability in the foam structure, in particular of salt mixtures, by gassifying of a conditioned pulp in the separation chamber with the aid of a gas injection device, from which the gassified pulp leaves in the form of a free jet.
2. The Prior Art
In such a known process for non-agitated flotation, which is known as pneumatic flotation, the conditioned pulp is pumped into a gassifying reactor under substantial pressure above atmospheric. In this case the gassing of the pulp is done by compressed air introduced from the outside. The gassified pulp leaves the gassifying reactor and enters the separation vessel and therein forms a free jet (article by A. Jungmann and U.A. Reilard concerning "Studies of the Pneumatic Flotation of Different Raw and Waste Substances with the Allflott System" ["Untersuchungen zur pneumatischen Flotation verschiedener Rohund Abfallstoffe mit dem Allflott-System"] published in "Aufbereitungstechnik" No. 8 (1988), p. 471.
The hydrophobic air-laden solid particles arrive on the surface of the separation vessel and form a foam, whereas the hydrophilic, non air-laden grains drop out of the free jet, or in part also out of the foam, sink and are drawn downwards as flotation residue.
In this process when the gassified pulp enters the separation vessel there is a correspondingly high flow speed which leads to turbulence in this area. This has the disadvantage, however, that a large portion of the grain bubble aggregates is destroyed by this turbulence, and therefore the grains can drop down, which entails corresponding losses in the flotation wastes.
To avoid this disadvantage, it has been proposed that the gassified pulp be introduced at high speed into an ascending pipe in which non-turbulent calming takes place and consequently a corresponding reduction in the flow energy occurs (see article by A. Jungmann and U.A. Reilard concerning "Studies of the Pneumatic Flotation of Different Raw and Waste Substances with the Allflott System" ["Untersuchungen zur pneumatischen Flotation verschiedener Rohund Abfallstoffe mit dem Allflott-System"] published in "Aufbereitungstechnik" No. 8 (1988), p. 473).
This system has the disadvantage, however, that in the area of the introduction of the free jet substantial turbulence builds up as a result of the pressure ratios prevailing there, which lead partly to backflow. This means, however, that the grain bubble aggregates do not arrive by the shortest route into the foam layer, which has the disadvantage that the air bubbles can be destroyed or separated and consequently the yield of useful flotation product is correspondingly smaller. (See also DE-OS 31 11 506, DE-PS 38 01 905).